1. Field of the Invention
This invention relates to a production method for a discrete structure substrate of a silicone semiconductor wafer having two-layer structure in which one side thereof is a diffusion layer and the other side is a non-diffusion layer. More specifically this invention relates to a production method for a discrete structure substrate requiring an excellent crystallinity in which a dislocation density measurable on the surface of the non-diffusion layer is less than 5000 pieces/cm.sup.2 on average, for use in transistors, diodes and the like. Further this invention specifically relates to a production method for a discrete structure substrate, in which diffusion is carried out under a raw material wafer thickness adjusted and determined by a dislocation density required when a discrete structure substrate is formed, so as to control an occurrence of a dislocation in the non-diffusion layer which may occur during the diffusion and the required dislocation density is satisfied finally when a discrete structure is manufactured to a predetermined dimension.
2. Description of the Prior Art
Conventional Method (1)
A conventional production method for a discrete structure substrate comprises the steps of:
preparing a raw material wafer subjected to a predetermined pretreatment; PA1 forming a diffusion layer having a predetermined depth from both sides of the wafer by diffusion method; and PA1 removing the diffusion layer on one side of the wafer. PA1 preparing a raw material wafer subjected to a predetermined pretreatment; PA1 forming diffusion layer having a predetermined depth from both sides of the wafer by diffusion method; and PA1 cutting the wafer along the center in the wafer thickness direction.
After that, a discrete structure substrate having a predetermined diffusion layer thickness (Xj) and a non-diffusion layer thickness (Xi) is produced.
Therefore, the raw material wafer thickness is product thickness (Xj+Xi) plus a minimum mechanical processing thickness including removal of the diffusion layer on one side.
Conventional Method (2)
Because, according to the above conventional method, one of the diffusion layers formed on both sides of the wafer is removed so that consequently half of the diffusion layers is wasted, recently a following method has been used. This method comprises the steps of:
According to this method, finally two pieces of the discrete structure substrates having a predetermined diffusion layer thickness (Xj) and non-diffusion layer thickness (Xi) are produced.
Therefore, the raw material wafer thickness is twofold of the product thickness (Xj+Xi) plus cutting thickness and minimum mechanical processing thickness on each cutting face.
This method does not look to lead to reduction of raw material because a thick wafer is used although two pieces of the discrete structure substrate can be obtained. However, for the reduction of the raw material, a loss thereof caused when a wafer is cut from an ingot must be additionally considered and so this method ensures the reduction of the raw material.
The conventional methods (1), (2) have been described. In any case, the raw material wafer thickness before diffusion is product thickness (thickness of a discrete structure substrate) plus minimum mechanical processing thickness (consequently, cutting dust) for obtaining a predetermined product dimension.